1. Field of the Invention
This invention is related to the addition of hydrogen and carbon monoxide to allyl alcohol to obtain 4-hydroxybutanal in the presence of a catalyst comprising a rhodium carbonyl catalyst with excess phosphine and is more particularly related to such a reaction conducted in the presence of a particular solvent which allows recovery of the product by water extraction, leaving the rhodium catalyst solution behind. Such a system provides excellent separation of the product from the phase containing the expensive rhodium catalyst. Only trace amounts of rhodium are lost to the product-containing phase.
2. Description of Related Processes in the Field
The compound 4-hydroxybutanal is an important intermediate for producing 1,4-butanediol. A number of methods have been discovered for hydroformylating various unsaturated compounds such as allyl alcohol to useful products such as 4-hydroxybutanal.
U.S. Pat. No. 3,980,670 discloses a process for manufacturing methacrylic acid and butyrolactone by hydroformylation of allyl esters of lower carboxylic acids in the presence of rhodium carbonyl complex catalysts and inert organic solvents, followed by oxidation of the resulting formyl compounds with molecular oxygen to produce 4-acetoxy-n-butyric acid and 3-acetoxy-isobutyric acid as the major products. See also German Offen. No. 2,106,243 to BASF. Unsaturated compounds such as propylene may be hydroformylated by means of rhodium/triphenylphosphine/carbonyl complexes formed in situ using a special preforming step described in U.S. Pat. No. 4,400,549.
In an article entitled "1,4-Butanediol via Hydroformylation of Allyl Alcohol", Chem. Systems; PERP 4th Quarterly Report, April 1982, there is disclosed a process for producing 1,4-butanediol via gas-phase hydroformylation of allyl alcohol using a supported liquid phase metal-organic catalyst. This reaction involves four steps.
In U.S. Pat. No. 3,929,915 there is disclosed a 3-step process for preparing 1,4-butanediol wherein the starting material is acrolein; the reaction conditions are conventional and several intermediate compounds are formed.
Even more on point is the following patent, U.S. Pat. No. 4,064,145, which describes a method for producing tetrahydrofuran and 1,4-butanediol by reacting synthesis gas with allyl alcohol under hydroformylation conditions in the presence of a rhodium carbonyl-phosphine catalyst complex and various inert solvents such as organic aromatics, aliphatic hydroxylic organic solvents, etc. In this patent, the allyl alcohol conversion was reported to be 99% and 4-hydroxybutanal was typically obtained in 87 wt% yield. Here there is not a desirable level of accounting for the rhodium catalyst. Also the amount of triphenylphosphine used, compared to the solvent and catalyst, is fairly large. Additionally, with the solvent used in this case two steps are necessary for extraction. The major by-product was 2-methyl-3-hydroxypropanal (12 wt%). A rhodium catalyst complexed with special bisphosphine monoxide ligands is taught as catalyzing the hydroformylation of olefinic compounds in the presence of an organic solvent according to U.S. Pat. No. 4,400,548. Again, two phase solvent systems are not disclosed.
U.S. Pat. No. 4,221,726 discloses a process for producing 1,4-butanediol by selectively hydrogenating acrolein to a product mixture of allyl alcohol and residual acrolein in a 2:1 ratio, converting the mixture to acrolein diallyl acetal under acidic conditions, selectively hydroformylating the acrolein diallyl acetal to a trialdehyde and reacting the trialdehyde under substantially neutral hydrolysis/hydrogenation conditions to yield 1,4-butanediol.
In J. Org. Chem., Vol. 45 (1980), 2132, C. U. Pittman, Jr. et al. disclose the hydroformylation of allyl alcohol to 4-hydroxybutanal and 3-hydroxy-2-methylpropanal using HRh(CO)(PPh.sub.3).sub.3 and its polymer-bound analogues. The selectivity of normal/ branched products was studied as the function of reaction parameters and ligands employed. The highest normal/branched selectivities were reported with 1,1'-bis(diphenylphosphino)ferrocene at 80%. Hazardous benzene and o-xylene solvents were generally used.
In J. of Mol. Cat., Vol. 11 (1981), 233-246, N. A. deMunck reported a heterogeneous gas phase hydroformylation of allyl alcohol using a supported HRh(CO)(PPh3)3 catalyst. A very high selectivity to 4-hydroxybutyraldehyde (97%) was achieved. However, the process is limited to only about 20% allyl alcohol conversion.
Kuraray disclosed the hydroformylation of allyl alcohol using a rhodium catalyst in an organic solvent such as benzene and toluene and a diphosphinoalkane. The overall n-/iso-ratio of the products was 86.6/13.4, (Kuraray, Japan. Pat. Open. No. 29412/1976, and No. 106407/1979. In additional patents (Kuraray, Japan. Pat. Open, No. 84508/1979 and British Patent No. 1,493,154, 1977) to Kuraray, a modified Raney catalyst was claimed for the hydrogenation of hydroxybutyraldehydes into 1,4-butanediol and 2-methyl-1,3-propanediol.
It is known in the art that allyl alcohol can be hydroformylated to .gamma.-hydroxybutyraldehyde in an aromatic hydrocarbon solution containing a rhodium complex catalyst and large excess of triphenylphosphine. The reaction products are extracted continuously with water and fed into a hydrogenation reactor containing a modified Raney nickel catalyst where the aldehydes are converted to corresponding alcohols, including 1,4-butanediol. See M. Tamura and S. Kumani; Chem. Econ. & Eng., Rev.; 12 #9 Sept. 1980; p. 32.
Many of the systems described above lack good conversions of the unsaturated reactant compound and/or good selectivity to the desired product. Further, recovery of expensive rhodium catalysts is a problem in many of these processes. It would be an advance in the art if a method could be devised for hydroformylating compounds such as allyl alcohol, while simultaneously solving the conversion, selectivity and catalyst recovery problems, and at the same time allowing isolation of the desired aldehyde product in reasonable purity and rate.